JPS58101804A - High performance pneumatic tire - Google Patents

Abstract

PURPOSE:To enhance the dimensional stability and uniformity of tires, by obtaining carcass plies including cords formed of filaments made of highly polymerized polyester and each having central and outer surface parts which are different in the birefringence and as well by using predetermined steel cords. CONSTITUTION:There are prepared filaments made of highly polymerized polyester containing more than 85% of ethyleneterephthalate component and having an ultimate viscosity of more than 0.8, which have a birefringence ratio between the outer surface part and the central part, of 1.03 to 1.15. These filaments are twisted so that the twist coefficient which is determined by an averaged twisting number of first and final twists or the like, is within a range between 800 to 2,500, and polyester cords having a dimensional stability coefficient which is represented by the sum of the elongation rate upon load of 2.3g/d and the dry heat contraction coefficient when the filaments are heated at 150 deg.C for 30min, of less than 8.5%, are used as carcass plies. Further, substantial part of element wires forming steel cords is made of steel material having a predetermined tensile strength and having a carbon content of 0.75 to 0.85wt%.

Description

[Detailed description of the invention] This invention relates to a pneumatic tire with excellent performance.

Multifilament yarns such as rayon, nylon, and polyester, or cords made of heated steel wire are used as reinforcing materials for pneumatic automobile tires, and the carcass of the tire is made of plies coated with rubber on these cords. Among the tires mentioned above, tires using nylon cords have the disadvantage that if they are left on a car for a long time, they will deform due to contact with the ground, causing so-called spot flats, and the spot flats will make the ride uncomfortable when you start driving again. In addition, rayon cords have low strength and steel cords have a large weight per detachment force. In contrast, polyester hoods have become widely used in recent years as they do not have the above drawbacks. However, motorway maintenance
There have been requests to improve the quality of polyester cords, and some issues have been raised. Chief among these problems is improving the dimensional stability and uniformity of the tire without compromising its fatigue resistance.

When using a tire that uses polyester cord for the carcass ply, when compressed air is injected into the tire cavity formed by attaching the rim to the bead of the tire, tension is applied to the cord and it stretches. This causes so-called inflation growth in which the tires are inflated. Along with this inflation growth, the tread rubber and side rubber are also stretched, resulting in a decrease in the wear resistance and crack resistance of the tire. Therefore, in order to reduce inflation growth, it is desirable to reduce the constant load elongation rate of the polyester cord.

On the other hand, in the manufacturing process of tires, for example, radial tires, a large number of arranged cords are coated with rubber and then cut in a direction perpendicular to the length of the hood. 1 to 10 side hoods are overlapped and joined to make a long cut cord, and this cut cord is cut to a certain length along the cord, and a cord tube drum of a fixed length is formed at the dent - 1 above. ~5 pieces are overlapped and joined to form a cylindrical carcass ply, and the open ends of the carcass ply are folded back and locked so as to wrap around the annular bead assemblies in contact with each of the open ends. Next, the diameter of the bead assembly is expanded while narrowing the interval to form a toroidal shape, and then a belt bridle, tread rubber, and side rubber are polymerized on the outer surface of the carcass ply to form a green tire, and this green tire is placed in a mold. Then, the inside of the green tire is pressurized with hot water or steam to extend the cord, which is heated from the inside and outside of the tire to vulcanize and mold. Then, compressed air is sealed into the tire cavity to prevent the cord from shrinking. In this state, the tire is cooled through so-called post-inflation, and then the tire is removed from the mold.

There is no major difference between the above manufacturing process and the manufacturing of bias tires.

In the upward tire manufacturing process &4, the cutting cord and the joint of the cutting cord during carcass ply formation are more rigid than other parts. Furthermore, if there are variations in the intervals and angles of the cord arrangement, when forming a cylindrical carcass ply into a toroidal shape, the proportion of expansion of the portion with high rigidity becomes small, resulting in a large difference in rigidity. As described above, the locally non-uniform stiffness of the carcass ply results in non-uniform tension acting on the hood during the above-mentioned post-inflation, resulting in non-uniform elongation of the hood. In addition, the rise in tire temperature during vulcanization varies depending on the thickness of the rubber, and the temperature distribution is not necessarily uniform, resulting in uneven heating shrinkage of the cord, and this uneven heating shrinkage is caused by
Coupled with the local non-uniformity of the stiffness of the tire, the elongation of the cord becomes non-uniform during the above-mentioned post-inflation, and the non-uniformity of the elongation of the hood causes local non-uniformity of the stiffness of the tire. Let's encourage it even more. When a car is driven with tires that have locally uneven stiffness as described above, the amount of deflection periodically builds up, causing abnormal vibrations that worsen ride comfort and further exacerbate the unevenness. If it becomes too large, the vehicle will periodically shake and become unstable. Since the non-uniformity of the tire in the tire manufacturing process described above is due to the high dry heat shrinkage rate of the polyester cord, it is desired that the dry heat shrinkage rate of the cord is low.

As an indicator of the dimensional stability of the hood, the dimensional stability is the sum of the elongation rate (%) under a load of 2.89/4 and the dry heat shrinkage rate (%) when heated at 150°C for minutes. It is expressed as a coefficient. However, the constant load elongation rate and dry heat shrinkage rate I!
The relationship is contrary to the law of 'i', and if the constant load elongation rate is increased, the dry heat shrinkage rate is decreased. For example, 1 made of conventionally used polyethylene terephthalate with an intrinsic viscosity of 0.9.
The dimensional stability coefficient of a cord with 500 denier/2 cords and a twist coefficient of 2190 is in the range of 9.0 to 9.5, and varies depending on the heating conditions. ['J' Even if the heavy elongation rate is decreased, the dry heat shrinkage rate increases, but the dimensional stability coefficient does not change.

As mentioned above, in order to obtain a tire with excellent uniformity, a polyester cord with a small constant load elongation rate and a small dry heat shrinkage rate, that is, a small dimensional stability coefficient, is required. If the cord is heat-treated for a long time in order to reduce the stability coefficient, the strength and fatigue resistance of the hood will be significantly reduced, and the performance as a tire hood will not be obtained. In addition, in order to reduce the dimensional stability coefficient, if a polyester with a relatively low degree of polymerization with an intrinsic viscosity of 0.8 or less is used as a raw material, or if the twist coefficient is reduced, the fatigue resistance will decrease. You won't get any useful code.

As a result of intensive research into the relationship between the degree of crystal orientation and dimensional stability of polyester cords with a high degree of polymerization, the present inventors found that
A tire manufactured using a filament with refraction between the center and the surface has good dimensional stability, and a tire whose carcass is formed from a cord with good dimensional stability does not suffer from the above-mentioned tire problems. I learned that it can solve the problem.

Based on the above findings, the present applicant has previously developed a polyester with a high degree of polymerization that contains 85 mol% or more of ethylene terephthalate component and has an intrinsic viscosity of 0.8 or more. The ratio is 1.08-1.
15 using the formula x = T x , nV
(K twist coefficient, T is the average number of twists of top and bottom twists per 10α, D is the indicated denier of the cord), heated to a range of 800 to 2500, and a load of 2.89/
(The dimensional stability coefficient expressed as the sum of the elongation rate (%) at 1:00 and the dry heat shrinkage rate (%) when heated at 150°C for 9 minutes is 8.
We proposed a pneumatic tire with excellent uniformity, characterized by using a polyester cord heat-treated to less than 5% as the tire carcass ply (Japanese Patent Application No. 56-806).
(See specification No. 46, hereinafter referred to as the first prior invention).

The filament forming the cord in this first prior invention is made of polyester containing 85 mol% or more of ethylene terephthalate, preferably polyethylene terephthalate, and containing 85 mol% or more of other components such as ethylene isophthalate and ethylene benzoate. It may also be a copolymerized polyester containing. The above polyester is a high polymerization degree polyester with an intrinsic viscosity of 0.8 or more measured at 6°C using ornchlorphenol as a solvent, and if the intrinsic viscosity is less than 0.8, a cord with a small dimensional stability coefficient can be obtained. It has low fatigue resistance and strength, and tires using it have poor durability.

The above-mentioned high polymerization degree polyester is spun and drawn at a relatively high tension so that the degree of orientation of the molecular chain axis in the fiber axis direction varies locally along the fiber radial direction.
The birefringence at the surface of the fiber is greater than that at the center.

In this first prior invention, the ratio of the birefringence of the surface portion to the birefringence of the filament center is 1.08 to 1.15.
A filament in the range of is selected. If the birefringence ratio is less than 1.08, the dimensional stability coefficient becomes large and the uniformity of the tire decreases, and if the birefringence ratio exceeds 1.15, the degree of orientation becomes relatively low. This reduces the strength of the tire cord.

A filament having a birefringence ratio within the above range can be obtained by appropriately setting conditions such as spinning speed, stretching ratio, and fixed value in spinning and drawing.

The thickness of the filament is preferably in the range of 1.6 to positive denier.

The twist coefficient when forming a cord by bundling and heating the above filaments is expressed as Txf, where T is the first twist in which multiple filaments are used as strands, and the final twist in which multiple filaments are used as a hood. and each code 1o
The average number of twists per clI is 1 or D is the indicated denier of the cord. Twisting coefficient: 800-2500
, preferably in the range of 1,800 to 2,800; if the twist coefficient is less than 800, the fatigue resistance will be low, and if it exceeds 2,500, the load elongation rate will increase and the uniformity of the tire due to inflation growth will decrease.

The above-mentioned hood is immersed in a latex adhesive solution, dried, and then heat-treated to improve adhesion to rubber.

The heat treatment temperature is preferably 220 to 250°C and the time is preferably 1 to 8 minutes.
It will be translated at your convenience. Generally, when the heat treatment temperature is high and the time is long, the dimensional stability coefficient tends to decrease.

The pneumatic tire obtained by this III/prior invention is
It has excellent wear resistance and crack resistance, and the tire has good uniformity.1. Not only does the car have a comfortable ride, but it also has less hysteresis loss due to the tire's expansion due to internal pressure and repeated deformation due to compression when it touches the ground. Therefore, the temperature generated inside the tire is lowered, and the rolling resistance is reduced.

On the other hand, in recent years, pneumatic tires reinforced with steel cords have been used for high-speed mass transportation or for construction vehicles, but the steel hoods have a high specific gravity, which makes the weight of the tires heavy, and as a result, the fuel There was a problem that the amount of consumption increased. As a countermeasure to this problem, we are trying to reduce the weight of the tire by using special compounded rubber and reducing the thickness of the excess rubber, but if we reduce the amount of steel cord used, the safety factor of the tire will decrease. Therefore, the current situation is that we have no choice but to use the steel cord without reducing the amount.

Furthermore, in pneumatic tires reinforced with steel cords, stress concentration acts on the interface between the rigid steel cords and the flexible rubber, which tends to cause rubber peeling at the ends of the steel cords or between the breaker layers in radial tires. Ta. In addition, if conventional pneumatic tires reinforced with steel cords are left in hot and humid conditions for a long time, moisture will seep between the iron material of the steel cords and the surface plating layer, causing the pneumatic tires to peel off. There was a drawback that a peeling phenomenon occurred.

As a result of various studies on the strength of steel cords in pneumatic tires, the present inventors found that the strength of conventional steel cords is expressed by the following experimental formula.

A=-1771-1,84N+0.02N"
(2) In the above formula (1), T8 is the tensile strength of the steel cord (#), W is the weight per 1 meter of steel cord (q, 'm) S denominator Noah, 86H&u>ratio jlT
In equation (2), D is the diameter Cl11) of the strands forming the steel cord, and N is the number of strands forming the steel cord. And the empirical formula of (11, (2) above is N-8 to 60, l1 = 0.15 to 0.4t)
Applicable within the range w. If D is less than 015, it is not practical due to low industrial productivity and high cost, and if D exceeds 0.40ff, the rigidity of the steel cord becomes excessive and the tire is likely to peel off. As a result, fatigue resistance also decreases.

The number N of strands in the above equation (2) is defined as m core strands when the wires have different diameters and are formed by m core strands and n side strands. A strand is regarded as one wire, and N is applied to n+.

In order to solve the drawbacks of conventional pneumatic tires, the present inventors aim to reduce the weight of pneumatic tires by reducing the amount of steel cord used, reduce the fuel consumption of vehicles, and reduce the delamination of pneumatic tires. The above objective was achieved by improving the tensile strength of the steel A/cord with the aim of reducing failures due to this.

That is, the applicant previously proposed a pneumatic tire at least partially reinforced with steel cords, in which most of the strands forming the steel cords had a carbon content of 0.75.
~0.85 weight -, and the steel cord is formula % Formula % (2)
is the number of strands in the steel cord configuration, W is the weight per 1 m of the steel cord, e, and 'rsti tensile strength is 7.86, which indicates the specific gravity of iron. We have proposed a pneumatic tire with the following characteristics (see the specification of Japanese Patent Application No. 1266115/1989, hereinafter referred to as the second prior invention).

Note that the applicable ranges of N and D in the above (2) are as in the conventional formula described above.

In order to improve the tensile strength of the steel cord to the range expressed by formula (8) above, the carbon content in the iron material of the wire forming the steel cord is set to 0.76 to 0.85%, and the carbon content of the conventional steel cord wire is set to 0.76 to 0.85%. The carbon content (rlo) should be greater than 69 to 0.78%. If the carbon content is less than 0.75%, the tensile strength will be small and the object of the second prior invention cannot be achieved. Furthermore, it is extremely difficult to heat-treat a seven-wire rod with a carbon content exceeding 0.85%, and the resulting steel cord has poor abrasion properties, making it more likely to break when a pneumatic tire steps on a protrusion or the like.

Steel cord wires having the above carbon content are plated with brass to improve adhesion to rubber. The component ratio of the brass is preferably 60 to 70% copper and 80 to 40% zinc. The copper in the brass is 6
If it is less than 0%, the iron material is hard and the brass exhibits a β phase, making it impossible to draw the steel hood wire. Moreover, if the copper content exceeds 70, pinholes will occur when the steel cord wire is drawn, and the surface of the brass layer will become rough, which is undesirable. What is noteworthy about this second prior invention is that the bond between the steel cord strands with high carbon content and the brass coating is strengthened, so that even if the tire is left in high temperature and humidity, it will not work as before. There should be no breakage between the iron and the brass.

To wet-draw steel wire in a lubricating oil, the wire is drawn at a higher pressure than conventional low-carbon steel wire, so the brass is press-bonded to the steel wire in a wire-drawing die. This is thought to be due to the

If the tensile strength of the steel cord is smaller than the value calculated using formulas (2) and (8) above, the reinforcement performance of the tire will decrease, assuming the tire strength is constant, and this will reduce the effect of reducing tire weight and lower fuel consumption. The effect is not much different from that of tires using conventional steel cords, and the purpose of this invention cannot be achieved.On the other hand, the tensile strength is thicker than the above calculated value, and when the tire strength is constant, In order to maintain the same strength as a tire using steel cord, the amount of steel cord used can be reduced by the increase in tensile strength, but in this case, the stiffness of the tire and the stiffness of the rubber-steel cord composite are As a result, the tire resistance was 11! The quality of the tag decreases.

As mentioned above, the first prior invention and the second prior invention each have their own excellent effects, but there are tires in which the polyester cord of the first prior invention is used as a carcass ply and the conventional steel cord is used as a breaker. Tires with Sakihatsumachi's steel cord as a breaker and conventional polyester cord as a carcass ply have a so-called belt edge separation between the steel cord end at the breaker end and the rubber, which causes growth. This causes tire separation.

This invention combines the performance of both prior inventions by using the polyvinyl steel hood according to the 21st prior invention as a carcass ply and using the steel cord according to the 2nd prior invention as a breaker, which is fatal in terms of tire performance. An object of the present invention is to provide a pneumatic tire that prevents the occurrence of edge separation and has excellent performance.

This invention will be explained in detail below.

Example 1 A polyester cord (1500a/2 cords) obtained by spinning and drawing a highly polymerized polyethylene terephthalate having an intrinsic viscosity of 0.9 and setting the spinning and drawing conditions so that the degree of crystal orientation is different between the filament surface and the center. It was used as a carcass ply, and its performance is shown in Table 1 below. In addition, polyester cords with different cord manufacturing conditions are also listed in Table 1 as comparative examples.

In accordance with the chemical fiber tire cord test method of It was shown in

Next, the steel cord used for the breaker is JIS-0
8502(r) 5WR882A material (carbon content 0.7
5~0.85%) strand H22 is plated with brass,
4000 rp with puncher type double twister
Heat the steel cord with a twist pitch of 10H x 4 x
The performance of the above-mentioned strands and steel cords is shown in Table 2 below. Furthermore, the comparison tDf
T? bK 5WR872A material (carbon content 0.69-0
．． 78%) of the wire L22 produced in the same manner as above and the performance of the steel hood are also listed.

(blank below) Table 2 Ru.

A.

These are the cross-sectional area of the Aoi-j iron material and the cross-sectional area of the A4/i wire.

Radial tire 165-18 was manufactured using the polyester hood shown in Table 1 as the carcass layer and the steel cord shown in Table 2 as the breaker layer, and its performance is shown in Table 8 below.

The rubber composition used for tire manufacturing is as follows! This is kwk club.

Natural rubber 100 HAP 55Zn0
7 Stearic acid 1 Trimethyldihydroquinone polymer 2 stoj
8 Resorcinol 2.5 Melamine derivative 25 Cobalt naphthenate 2.5 Sulfur
4 Dicyclohexylbenzthiadylsul7enamide
0.8 (blank below) Table 8 T 1 kl Since the amount of steel hood in the breaker is small, the tire becomes m-less, and the polyester cord in the carcass has a small hysteresis loss, so the synergistic effect makes the tire The transfer resistance ratio and fuel consumption ratio of the tires have been dramatically improved, and because the tires have good uniformity, belt edge separation, which tends to occur at the breaker end of carcass-bonded products, is less likely to occur, further improving high-speed durability. It is excellent.

The tire uniformity in Table 8 above is based on the automobile standard established by the Society of Automotive Engineers of Japan, TASO-c607, and a tire with an internal pressure of 2 kg/d is placed on a drum with an outer diameter of 851.1 kg and a load of 366 kg.
g and rotated at 60 rpm, the magnitude of the variation in force in the radial direction of the tire was measured, and the average measured value was expressed on a 5-level scale, with grade 5 being the best in uniformity. The high-speed durability of tires meets the US automobile safety standard FMVSS 1.
09, internal pressure air 1.7 & 9/d.

The drum was run at a speed of 80 b/hr while adding a predetermined load at predetermined intervals, and the time until tire failure was measured. Most of them used the fxn conventional code and were expressed as an index with the measured value of 9T4 set as 100. The transfer resistance ratio is 1600 Ce with the above test tire installed.
A passenger car was driven at a speed of 60 m/hour at a test drive in Tsuno-cho, Miyazaki Prefecture, owned by the applicant, and when it reached a certain point, the clutch was disengaged, the engine stopped, and the distance traveled by inertia was measured. The coasting distance of the tire T4 is 10
This is the value when it is set to 0. The fuel consumption ratio is a value when the fuel consumption required for traveling 411b+ of the above-mentioned driving test tooth is set to 100 of the fuel consumption of T4.

Moist heat coverage is the rate of rubber adhesion to the steel cord when each tire is left in the air at 70°C and 95% RH for two weeks, then disassembled and the breaker is peeled off.

In the above moist heat coverage test, when observing the peeled surface, it was found that in the conventional tire T4, the brass plating layer adhered to the rubber side on the exposed surface of the steel cord, and peeling between the iron and the brass was observed. Therefore, the copper content on the rubber side and the steel cord side was measured using an X-ray microanalyzer Ir on the peeled surface where no rubber was attached to the brass layer, and the results are shown in Table 4.

Table 4 Tire symbol Tl 'T4 cord side steel
(Support)) 98.0 67.1 Copper on the rubber side (1) 2.082.9 As seen in Table 4 above, T1 of this invention has a strong bond between the iron and the brass. On the other hand, the conventional product T4 has a small bond. It is completely unexpected that the increased strength of the steel cord of the present invention contributes to a stronger iron-brass bond.

Example 2 One layer of carcass ply was made of polyester cord (1500 denier/2 pieces) made from highly polymerized polyethylene terephthalate as a raw material and obtained under conditions such that the degree of crystal orientation was different between the center and surface of the filament. Radial tires T6 and T7 of size 1558P+18 are made using the same steel cord as the tire T1 of Example 1 as a breaker.
was manufactured. In addition, tires similar to those in Example 2 with different polyester cord manufacturing conditions were manufactured to obtain Tire T of Comparative Example.
8, T9, TIO, and the tires of Example 2 are T6, T
The polyester needle manufacturing conditions and tire performance of tires T3, T9, and TIO of Comparative Examples 7 and B are shown in Table 5 below.
show.

(Blank below) 1 5th
Number 5 above the table! Step 1: Sidewall unevenness C: Fill the tire with internal pressure air of 2.2 phantom/d, and then measure the depth of the groove-like recesses in the radial direction on the sidewall portion, which are formed when the tire is filled, with a caliper to determine the occurrence of the recesses. If there is no depth, it is grade 8, if the depth of the four parts is 0.08111 or less, it is grade 2, and if the depth of the concave part is 0.08.
Those with a diameter of m or more were designated as 1st grade. Tire heat generation was measured in a tire high-speed durability test based on FMVSS109 as explained in Example 1 above.After running under the maximum load condition, a needle was inserted into holes previously drilled in the side edges and center of the tire tread. The humidity at the bottom of the tread was measured by inserting a thermistor thermometer, and the average value of the difference in temperature between the bottom of the tread and the room temperature between the side edges and the center was shown.

As can be seen in Table 5 above, the tires T6 and T7 of the example with birefringence ratios of 1 and 10 have small dimensional stability coefficients even if the twist coefficients are different, and they have the same excellent tire performance. have. However, Comparative Tires T8 and T9, which were manufactured using highly polymerized polyethylene terephthalate under conditions such that there was no difference between the center portion and the surface portion of the filament, had different dimensional stability coefficients due to the difference in twist coefficient. Tires T6 and T7 of Example 2 do not have sidewall irregularities and have the same tire durability as or better than the tire TIO of the comparative example, and tire heat generation and tire transfer resistance are lower than that of the comparative tire. is better than.

The edge separation in Table 5 above is the result of observing the condition of the edge separation by disassembling the breaker part of the tire after the high-speed durability test of the tire. There is no or little edge separation.

Example 3 4-ply polyester cord pm1 of Example 1, number of ends n/261E1. Using the cord angle of 90 degrees as a carcass ply, wrap the side wire H around the core wire HMJ shown in Table 6 below to form 8 X O, 20 + 6 X
A radial tire 100QR2D-14PR for a truck bus was manufactured using an O.25 steel cord as a breaker.

The breaker cord conditions of this tire are shown in Table 6, and the breaker configuration and tire performance are shown in Table 7.

(Blank below) Table 6 R/Ro in Table 6 above indicates the ratio of the diameter R at the end of the steel cord to the diameter Ro at the center of the steel cord. The part is made of bamboo floating in the shape of a parasol.

As seen in Table 7 above, even large radial tires are lightweight, have good uniformity, have low rolling resistance, have excellent high-speed durability, and cause breaker edge separation. It has difficult performance.

Patent applicant: Toyo Rubber Industries, Ltd. Agent: Patent Attorney Takeo Sakano Yoshi 1) Tsukasa Tsukasa

Claims (1)

[Scope of Claims] [1] Consisting of a high polymerization degree polyester containing δ mol % or more of an engineered tylene terephthalate component and having an intrinsic viscosity of 0.8 or more, the ratio of the birefringence of the surface portion to the birefringence of the filament center is A filament with a diameter of 1.08 to 1.15 is
= T
The average number of twists of the first twist and first twist per hit (D is the indicated denier of the cord) is heated to a twist coefficient in the range of 800 to 2500, and the elongation rate at a load of 2.89/d and 150 ° C.
A polyester cord with a dimensional stability coefficient of 8.5% or less, expressed as the sum of the dry heat shrinkage rate when heated for J minutes, is used as the tire carcass ply, and most of the carbon-containing material that forms the steel cord is used as a tire carcass ply. It consists of an iron material with an amount of 0.75 to 086% by weight, and the formula % (in the above formula, D is the strand diameter fl of the steel cord, N is the number of strands in the steel cord configuration, and W is the number of strands per 1 m of steel cord). Arashisa 9.TS is a pneumatic tire with excellent performance characterized by using a steel cord as a breaker, which has a tensile strength calculated as follows: (7.86 in the denominator indicates the specific gravity of iron). [2] The pneumatic tire with excellent performance according to claim 1, wherein the highly enriched polyester is polyethylene terephthalate. [8] Steel cord strands are 60-70% copper and zinc J
- High-performance pneumatic tire according to claim 1 or 2, coated with a proportion of 40% brass. [4] Composite steel cord in which the core strand of the steel cord is made of iron material with a carbon content of 0.65 to 0.76%, and the side strand wire is made of iron material with a carbon content of 0.75 to 0.85%. A pneumatic tire with excellent performance according to any one of claims 1 to 8. [5] A pneumatic tire with excellent performance according to any one of claims 1 to 4, wherein the ends of the steel cord are dispersed in a broom-like shape.